The phenomenon that the battery discharging characteristics changes throughout the lifespan of a battery is often called battery ageing. The effect of battery ageing is often observed in the capacity decay and reduced efficiency. The known battery test techniques usually involve fully charging the battery followed by fully discharging to obtain the actual battery capacity. In general, the time required to test a battery ranges from 1 to 10 hours (1C to 0.1C, C stand for capacity), which causes much inconvenience for the user. Therefore, various researches are conducted by both academics and industry to improve the understanding of the battery condition in order to operate the battery within safety parametric boundaries to lengthen the battery lifespan and usage safety.
The common research techniques on battery ageing usually employ analysis tools to describe and define the problems encountered by the battery, followed by performing prediction on the battery characteristics and, finally, finding solutions to the battery ageing problems. Some of the descriptive tools include such as, remaining capacity (decay), impedance (1 kHz, DC-IR), equivalent circuit model (ECM), electrochemical impedance spectrum (EIS), and so on; and some of the prediction tools include such as, lifetime model, remaining usable life (RUL), and so on. Because the tools used in predicting the characteristics of ageing battery require a large amount of computation, such as, the lifetime model and RUL, efficiency becomes an important concern.
A disclosed technique uses state of charge (SoC) measurements, temperature and other parameters, as well as intelligent algorithm, to estimate the current ageing state of the battery. Another technique disclosed a method and system of estimating battery state and parameters (such as, impedance, voltage, current temperature, and so on) to estimate the state of charge and the state of health of the battery. Yet another technique disclosed a system and method for ensuring the state of health of the battery set, by charging the battery set to the fullest and then ensuring the open-circuit voltage of the battery set to ensure the state of health of the battery set.
In the aforementioned and current battery ageing studies, shortcomings exist in actual application tests. For example, the shortcoming of the current EIS technique may include: (1) long test time: a long duration to charge and discharge is required to measure the EIS in all states of charge of the battery; and (2) poor reproducibility: as the measurement requires reconnecting the measurement wires, the contact impedance will affect the accuracy of the measurements. Therefore, it is imperative to devise a technique to study battery ageing so that the battery can operate in a lower stress condition.